The present invention relates to an apparatus and a method for detecting misfires in an internal combustion engine, which apparatus and method detect misfires based on fluctuations in rotation of the engine. Particularly, the present invention relates to a technology for distinguishing which one of a single-cylinder misfire, a consecutive-cylinder misfire, and an intermittent-cylinder misfire is occurring in consecutively ignited three cylinders.
If ignition is missed, or if a misfire occurs, in a spark ignition type internal combustion engine, unburned fuel is discharged to an exhaust passage. This degrades emission and lowers the engine performance. Thus, a number of measures have been taken for preventing misfires. However, a misfire can occur despite the taken measures. It is therefore desired that a misfire be quickly and accurately detected.
Accordingly, various devices for detecting a misfire have been proposed. For example, Japanese Laid-Open Patent Publication No. 10-318033 disclosed a misfire detecting apparatus for a multi-cylinder internal combustion engine. The misfire detecting apparatus detects three types of misfire in three cylinders that are consecutively ignited. That is, the apparatus detects a case where a misfire occurs in only one of three consecutive cylinders (single-cylinder misfire), a case where a misfire occurs in two consecutive cylinders (consecutive-two-cylinder misfire), and a case where a misfire occurs in nonconsecutive two cylinders with a normal combustion in the cylinder in between (intermittent-two-cylinder misfire).
In the above publication, it is assumed that a misfire occurs in the leading one of three cylinders to be ignited consecutively, a rotation fluctuation xcex94TN of the engine (crankshaft) has different patterns in the single-cylinder misfire, the consecutive-two-cylinder misfire, and the intermittent-two-cylinder misfire. FIGS. 14(a) to 14(c) show cases where ignition is executed in a first cylinder #1, a second cylinder #2, and a third cylinder #3 in this order after a normal combustion in a sixth cylinder #6, and a misfire occurs in the first cylinder #1. In FIGS. 14(a) to 14(c), xcex94T3 denotes a rotation fluctuation amount at the first cylinder #1, xcex94T2 denotes a rotation fluctuation amount at the second cylinder #2, and xcex94T1 denotes a rotation fluctuation amount at the third cylinder #3.
As shown in FIG. 14(a), in the single-cylinder misfire, where a misfire occurs only in the first cylinder #1, xcex94T3 is relatively great, and xcex94T2 and xcex94T1 are relatively small. As shown in FIG. 14(b), in the consecutive-two-cylinder misfire, where a misfire occurs in the first cylinder #1 and the second cylinder #2, xcex94T3 and xcex94T2 are relatively great, and xcex94T1 is relatively small. As shown in FIG. 14(c), in the intermittent-two-cylinder misfire, where a misfire occurs in the first cylinder #1 and the third cylinder #3, xcex94T3 is relatively great, xcex94T2 is relatively small, and xcex94T1 is relatively great.
The apparatus of the publication determines the type of the occurring misfire based on the above described patterns of rotation fluctuations. That is, the apparatus compares the rotation fluctuation amounts xcex94T1, xcex94T2, xcex94T3 with one another using predetermined constants k1, k2. When an inequality xcex94T3xc2x7k1 less than xcex94T1 is satisfied, the apparatus determines that the intermittent-two-cylinder misfire is occurring. When the inequality xcex94T3xc2x7k1 less than xcex94T1 is not satisfied, and an inequality xcex94T3xc2x7k2 less than xcex94T2 is satisfied, the apparatus determines that the consecutive-two-cylinder misfire is occurring. When the inequality xcex94T3xc2x7k1 less than xcex94T1 and the inequality xcex94T3xc2x7k2 less than xcex94T2 are both satisfied, the apparatus determines that the single-cylinder misfire is occurring.
However, tests carried out by varying conditions such as the type of the engine and the running states of the engine, such as the engine rotation speed and the engine load, revealed that the above listed rotation fluctuation patterns are mere typical ones and that there are other various rotation fluctuation patterns.
For example, in the single-cylinder misfire shown in FIG. 14(a), the rotation fluctuation amount xcex94T2 at the second cylinder #2 can have a minus value, and the rotation fluctuation amount xcex94T1 at the third cylinder #3 can have a plus value. As for the consecutive-two-cylinder misfire shown in FIG. 14(b) and the intermittent-two-cylinder misfire shown in FIG. 14(c), various patterns other than the above listed ones can appear. These phenomena occur in, for example, in-line six cylinder engines, and particularly in an engine that has a sensor for detecting the engine rotation speed at one end of the row of the cylinders. One reason for this is that a rotation fluctuation caused by a misfire is affected and changed by a torsional resonance of the crankshaft before reaching the sensor, and it is therefore difficult to accurately detect the rotation fluctuation.
The misfire detection apparatus of the above publication determines the type of a misfire on the assumption that a rotation fluctuation pattern obtained based on detection values of the sensor matches with one of the typical rotation fluctuation patterns shown in FIGS. 14(a) to 14(c). Therefore, when a rotation fluctuation pattern during a misfire is different from the typical patterns, the type of the occurring misfire can be erroneously determined. To avoid erroneous determinations, the apparatus must be applied only to a limited types of engines. Also, the apparatus is only capable of detecting a misfire in a limited number of engine running states.
Accordingly, it is an objective of the present invention to provide an apparatus and a method for detecting a misfire in an internal combustion engine, which apparatus and method are capable of functioning in various rotation fluctuation patterns that appear due to a misfire.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a misfire detection apparatus for an internal combustion engine having a plurality of cylinders is provided. The apparatus selects three of the cylinders that are consecutively ignited as subjects of misfire detection, and defines the selected cylinders as a first subject cylinder, a second subject cylinder, and a third subject cylinder in an order of ignition. The apparatus is capable of detecting three types of misfire including a single-cylinder misfire, in which a misfire occurs only in the first subject cylinder, a consecutive-two-cylinder misfire, in which a misfire occurs in the first and second subject cylinders, and an intermittent-two-cylinder misfire, in which a misfire occurs in the first and third subject cylinders. The apparatus includes computation menas, first determination means, second determination means, and third determination means. The computation means obtains a rotation fluctuation amount of the engine at each of the first to third subject cylinders. The first determination means determines whether a misfire is occurring in the first subject cylinder based on the rotation fluctuation amount at the first subject cylinder. When it is determined that a misfire is occurring in the first subject cylinder, the second determination means determines whether the type of the occurring misfire is a single-cylinder misfire based on the rotation fluctuation amount at the second subject cylinder and the rotation fluctuation amount at the third subject cylinder. When it is determined that the type of the occurring misfire is not a single-cylinder misfire, the third determination means determines whether the type of the occurring misfire is a consecutive-two-cylinder misfire or an intermittent-two-cylinder misfire based on the rotation fluctuation amount at the second subject cylinder and the rotation fluctuation amount at the third subject cylinder.
In another aspect of the present invention, a misfire detection method for an internal combustion engine having a plurality of cylinders is provided. The method includes: selecting three of the cylinders that are consecutively ignited as subjects of misfire detection, and defining the selected cylinders as a first subject cylinder, a second subject cylinder, and a third subject cylinder in an order of ignition; and determining a occurring misfire to be one of three types of misfire including a single-cylinder misfire, in which a misfire occurs only in the first subject cylinder, a consecutive-two-cylinder misfire, in which a misfire occurs in the first and second subject cylinders, and an intermittent-two-cylinder misfire, in which a misfire occurs in the first and third subject cylinders. The determining of the misfire type includes: obtaining a rotation fluctuation amount of the engine at each of the first to third subject cylinders; determining whether a misfire is occurring in the first subject cylinder based on the rotation fluctuation amount at the first subject cylinder; determining whether the type of the occurring misfire is a single-cylinder misfire based on the rotation fluctuation amount at the second subject cylinder and the rotation fluctuation amount at the third subject cylinder when it is determined that the misfire is occurring in the first subject cylinder; and determining whether the type of the occurring misfire is a consecutive-two-cylinder misfire or an intermittent-two-cylinder misfire based on the rotation fluctuation amount at the second subject cylinder and the rotation fluctuation amount at the third subject cylinder when it is determined that the type of the occurring misfire is not a single-cylinder misfire.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.